The function of the nuclear envelope in regulating the uptake of endogenous protein into the nucleoplasm was studied using Xenopus oocytes. The envelopes were mechanically disrupted by puncturing the oocytes with fine glass needles. This resulted in a 10 fold increase in nuclear uptake of cytoplasmically injected 125I BSA, indicating that the permeability characteristics of the envelope were significantly altered. However, the puncturing procedure did not effect, either quantitatively or qualitatively, the nuclear uptake of endogenous polypeptides which were labelled with 3H-leucine. These results indicate that the accumulation of specific nuclear proteins is not controlled by the envelope but by selective binding sites within the nucleoplasm. This approach is currently being used to investigate the nucleocytoplasmic translocation of RNA. Studies are also planned to determine the distribution of oligosaccharides on the nuclear envelope. Ferritin-labelled wheat germ and Ricinnus communis agglutinins will be used to localize N-acetyl-D-glucosamine and D-galactose residues, respectively. In addition, radioactive lectins will be used to identify specific envelope glycoproteins on polyacrylamide gels.